A baseball cap including features for stabilizing the cap in a moving stream of air. The cap includes a modified bill having a downforce generator configured to create a relatively stagnate recirculation zone between the downforce generator and the head covering. This recirculation zone tends to negate the lifting effect found in prior art bills. The invention preferably includes a vent through the bill. The vent is located behind the downforce generator, to connect the underside of the bill to the recirculation zone formed in the wake of the downforce generator. The vent is selectively closed by a flexible flap. The flap remains closed to prevent rain from passing through the vent. However, if pressure beneath the bill significantly exceeds pressure above the bill, the vent opens to equalize the pressure. This action prevents the creation of a net lifting force which might lift the cap off the wearer's head.
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1. A baseball cap, comprising:
a. a head covering, including a forward region;
b. a bill extending outward from said forward region of said head covering, said bill having a leading edge distal to said head covering and a trailing edge proximal to said head covering;
c. a downforce generator, extending upward from said bill, wherein said downforce generator extends only part of the way from said leading edge of said bill to said forward region of said head covering and ending in a trailing portion, thereby creating a gap between said trailing portion of said downforce generator and said forward region of said head covering with said gap having a distance across said gap;
d. a vent, extending through said bill into said gap, with said vent having a forward portion and a rearward portion;
e. a flexible flap lying across said vent, with said flexible flap having a forward edge and a trailing edge;
f. said forward edge of said flexible flap being joined to said bill proximate said forward portion of said vent;
g. said flexible flap being bendable into an open configuration wherein said trailing edge of said flap is approximately parallel to said forward region of said head covering, thereby forming a throat between said flexible flap and said forward region of said head covering, said throat having a distance across said throat;
h. wherein said distance across said throat is between about ½ and ¼ said distance across said gap;
i. wherein said downforce generator has a middle portion, a first side extreme, and a second side extreme; and
j. wherein said downforce generator has a splitter located in said middle portion, with said splitter being configured to divide said air flow into a first portion directed toward said first side extreme and a second portion directed toward said second side extreme.
2. A baseball cap as recited in
a. said downforce generator is a thin structure attached along said leading edge of said bill, thereby forming a cavity between said downforce generator and said bill: and
b. said downforce generator includes a drain passing through said downforce generator, thereby draining said cavity.
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This application is a continuation in part of U.S. patent application Ser. No. 12/154,562, which was filed on May 23, 2008 now abandoned. The parent application listed the same inventor.
Not Applicable.
Not Applicable
1. Field of the Invention
This invention relates to the field of headwear. More specifically, the invention comprises a baseball cap having a modified bill configured to produce downforce when the cap is placed in a moving airstream.
2. Description of the Related Art
The “baseball cap” is one of the world's best known hats.
Those familiar with the art will know that such hats are made using a variety of technique. The example of
In this expression, v stands for the flow velocity at a given point, g stands for gravitational acceleration, h stands for the height above a reference plane, P stands for the pressure of the air at a given point, and ρ stands for the density of the air at a given point.
From this equation one may easily discern the fact that when a compressible fluid is flowing past an object at subsonic speeds, the faster the flow is sin a particular region the lower the pressure will be in that region. When looking at
The flow passing under the bill, however, impacts the wearer's face 16. This produces a recirculation area denoted as stagnation region 20. The flow in this area is relatively slow. Thus, from Bernoulli's equation, one may accurately predict that the air pressure in the area beneath the bill will be greater than the air pressure in the area above the bill. The result is the creation of lift 24, which tends to lift the cap free of the wearer's head.
Prior hat designers have accounted for this phenomenon by angling the bill downward as shown. The downward angle has the effect of an airfoil having a negative angle of attack. The flow over the top therefore creates downforce 22. If the magnitude of downforce 22 exceeds that of lift 24, then the hat will stay on. Of course, the motion of the wearer's head alters the bill's angle of attack. If the user inclines her head slightly, downforce 22 will be greatly reduced. This will likely be the instant when the moving airstream lifts the cap free of the wearer's head and carries it away.
The loss of such a cap is a significant inconvenience. This is particularly true in a boating situation, where the hat is likely to blow overboard and be lost. Prior art designers have attempted to remedy this known problem in a variety of ways. For example, some caps have incorporated a bill having a hinged vent flap. The vent flap pivots upward if the pressure difference between the region beneath the bill and above the bill becomes large enough. Other designs have incorporated one or more fixed vents through the bill. Still other designs have incorporated a bill with a severe downward angle, so that the bill's angle of attack remains negative throughout the range of motion of the user's head.
While these prior art designs have in part remedied the problem, no prior art design has produced a good solution while still maintaining the conventional benefits of the traditional baseball cap. The present invention seeks to remedy these shortcomings.
The present invention is a baseball cap including features for stabilizing the cap in a moving stream of air. The cap includes a modified bill having a downforce generator configured to create a relatively stagnate recirculation zone between the downforce generator and the head covering. This recirculation zone tends to negate the lifting effect found in prior art bills.
The invention preferably also includes a vent through the bill. The vent is located behind the downforce generator, so as to connect the underside of the bill to the recirculation zone formed in the wake of the downforce generator. The vent is selectively closed by a flexible flap. The flap remains closed to prevent rain from passing through the vent. However, if pressure beneath the bill significantly exceeds pressure above the bill, the vent opens to equalize the pressure. This action prevents the creation of a net lifting force which might lift the cap off the wearer's head.
REFERENCE NUMERALS IN THE DRAWINGS | ||||
10 | baseball cap | 12 | head covering | |
14 | bill | 16 | face | |
18 | high velocity region | 20 | stagnation region | |
22 | downforce | 24 | lift | |
26 | stay-on cap | 28 | modified bill | |
30 | downforce generator | 32 | splitter | |
34 | vent | 36 | flap | |
38 | drain | 40 | upper pressure | |
42 | lower pressure | 44 | flap attachment | |
46 | free end | 48 | secondary downforce | |
50 | forward region | 52 | leading edge | |
54 | trailing edge | 56 | gap | |
58 | cavity | 60 | first lateral extreme | |
62 | second lateral extreme | 64 | trailing portion | |
66 | closing pressure | 68 | throat | |
70 | exit | |||
The central concept of the present invention is to provide a system that prevents moving air from forcing a cap off a wearer's head by providing an uplifting force on the cap's bill. At the same time, the system should retain the normal sun shading and moisture channeling capabilities of a conventional cap. In order to achieve these objectives, the invention features a vent through the bill which is selectively opened and closed by a moveable flap.
The flap operates in conjunction with a downforce generator located on top of the bill. The geometry of the vent, the flap, the cap, and the downforce generator combine to selectively create (1) a first state in which the flap opens to allow flow through the bill when needed to keep the hat in place; and (2) a second state in which the flap is forced closed in order to restore the normal functions of the bill. The automatic transfer between these two states is referred to as “active load relief,” meaning that the cap automatically changes its configuration in order to hold the cap in position on the wearer's head.
The width of bill 14 is preferably between about 15 cm and 25 cm. The length of the bill is preferably between about 6 cm (a “short bill”) and about 14 cm (a “fishing bill”). The width and length of vent 34 is obviously less than that of the bill. The width of vent 34 is between about 12 cm and about 21 cm. The slot is preferably between 1.5 cm and 3 cm across. Flap 36 preferably covers the entire slot. Thus, flap 36 is preferably between about 13 cm and about 22 cm wide. It is preferably between 1.6 cm and 4 cm across.
The presence of gap 56 creates a recirculation zone behind the trailing edge of the downforce generator. The airstream impacting the upwardly inclined forward surface of the downforce generator creates downforce 22 (through stagnation pressure of the air impacting the device). Downforce 22 obviously tends to hold the hat down on the user's head. The creation of the recirculation zone in gap 56 tends to create relatively high pressure in this region, which places secondary downforce 48 on the upper surface of flap 36 and tends to retain the flap in the closed position when the air is passing over the bill in the fashion shown in
Flap 36 is made of a flexible material. It is preferably attached to the bill by flap attachment 44 (which can be a sewn joint, an adhesive joint, etc.). The effect of this construction is that the leading edge of flap 36 remains in a fixed position with respect to the bill, but free end 46 can lift upward, thereby opening vent 34 and allowing flow to occur from below the bill to above the bill.
In the configuration shown in
In
In the scenario of
The relative scaling of the geometry of the vent, the downforce generator, and the cap is important to the operation of the device. Returning briefly to
This phenomenon is shown in
The flow through the venturi is governed by Bernoulli's Equation, which is restated below:
The left side of the equation represents a first position in the moving flow and the right side represents a second position in the moving flow. From the equation, one may easily perceive that as flow velocity increases, the pressure of the moving air decreases. The flow velocity is greatest in the region of throat 68 (as for any venturi) and as a result this is the region of lowest pressure. The flow velocity in the recirculating region behind flap 36 is nearly zero, and the pressure in that region is much higher. The differential pressure results in the creation of closing pressure 66, which tends to force the flap closed again.
The differential pressure created by the venturi effect causes the flap to close significantly faster than gravity alone. The result is that less pressure (under the bill) is required to open the flap than is required to hold it open. A quick up-lifting pressure is generally what blows the cap off the wearer's head. The present venturi design rapidly opens. However—unless a sustained flow is passing through the vent—it will rapidly close again. This means that the venturi design provides the desired rapid pressure relief while also quickly returning to the closed state in order to provide sun shade and rain exclusion.
In order to create the desired effect, the geometry of the flap and exit must be appropriately sized. In the embodiment of
The throat area is Wt·Lt, while the area of the exit is We·Le, where W is width, L is length, t stands for throat, and e stands for exit. If the length of the throat is the same as the length of the exit (which is roughly true), then the area ratio may be simplified to the distance across the exit divided by the distance across the throat. This ratio is preferably maintained between 2 to 1 and 4 to 1. Thus, in the embodiment of
Returning now to
Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As an example, although the invention has been illustrated with a thin walled downforce generator, a solid or thick-walled design made of lightweight foam material could be substituted. Many other variations will be apparent to those skilled in the art. Thus, the scope of the invention should be fixed by the following claims rather than any specific examples provided.
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